// 
// Copyright (c) 2004-2021 Jaroslaw Kowalski <jaak@jkowalski.net>, Kim Christensen, Julian Verdurmen
// 
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without 
// modification, are permitted provided that the following conditions 
// are met:
// 
// * Redistributions of source code must retain the above copyright notice, 
//   this list of conditions and the following disclaimer. 
// 
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution. 
// 
// * Neither the name of Jaroslaw Kowalski nor the names of its 
//   contributors may be used to endorse or promote products derived from this
//   software without specific prior written permission. 
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 
// THE POSSIBILITY OF SUCH DAMAGE.
// 

namespace NLog.Time
{
    using System;

    /// <summary>
    /// Fast time source that updates current time only once per tick (15.6 milliseconds).
    /// </summary>
    public abstract class CachedTimeSource : TimeSource
    {
        private int _lastTicks = -1;
        private DateTime _lastTime = DateTime.MinValue;

        /// <summary>
        /// Gets raw uncached time from derived time source.
        /// </summary>
        protected abstract DateTime FreshTime { get; }

        /// <summary>
        /// Gets current time cached for one system tick (15.6 milliseconds).
        /// </summary>
        public override DateTime Time
        {
            get
            {
                int tickCount = Environment.TickCount;
                if (tickCount == _lastTicks)
                    return _lastTime;
                else
                {
                    DateTime time = FreshTime;
                    _lastTicks = tickCount;
                    _lastTime = time;
                    return time;
                }
            }
        }
    }
}
